Positioning apparatus for article with portion determining portion of predetermined configuration

ABSTRACT

An article-positioning apparatus for precisely determining the location of an article either with respect to another article or with respect to a given reference. The article has a positiondetermining portion of a predetermined configuration. A prism which has the shape of a truncated pyramid is provided with opposed end faces one of which is smaller than the other with both of these end faces having the predetermined configuration of the position-determining portion of the article. An optical projector projects onto the smaller end face of the prism an image of the position-determining portion of the article, and the deviation of this image from a position of precise alignment with the smaller end face of the prism is determined so that the article can be positioned at a location where the image of the position-determining portion thereof is indeed precisely aligned with the smaller end face of the pyramid, whereupon it is known that the article is then precisely situated at the desired location.

United States Patent Nishikawa et al.

[54] POSITIONING APPARATUS FOR ARTICLE WITH PORTION DETERMINING PORTIONOF PREDETERMINED CONFIGURATION [72] inventors: Yuklyasu Nishlltawa,Saitarna-ken; Tsuneo Hldaka, Tokyo, both of Japan [73] Assignee: AsahiKogaku Kogyo Kahushiltl Keisha,

Tokyo-to, Japan [22] Filed: June 26,1970

211 App]. N0; 50,069

52 us. or. ..250/231a, 250/220 R, 356/152 51 Int. (:1. 5/34 581 Field 611........250/219 a, 21 1 J, 227, 216,

Vyce ..250/227 Wallmark ..250/2ll J 1 1 July 11,1972

3,432,671 3/1969 Edmonds ..250/2l6X Primary Examiner-Walter StolweinAttorney-Steinberg & Blake [57] ABSTRACT An article-positioningapparatus for precisely determining the location of an article eitherwith respect to another article or with respect to a given reference.The article has a positiondetermining portion of a predeterminedconfiguration. A prism which has the shape of a truncated pyramid isprovided with opposed end faces one of which is smaller than the otherwith both of these end faces having the predetermined configuration ot'the position-determining portion of the article. An optical projectorprojects onto the smaller end face of the prism an image of thepositiondetermining portion of the article, and the deviation of thisimage from a position of precise alignment with the smaller end face ofthe prism is determined so that the article can be positioned at alocation where the image of the position-determining portion thereof isindeed precisely aligned with the smaller end face of the pyramid,whereupon it is known that the article is then precisely situated at thedesired location.

9 Claims, 16 Drawing Figures P'A'TENTEDJUL 11 m2 3. 6 76 692 mvsw-ronsYUKIYASU NISHIKAWA BY TSUNEO HIDAKA ATT NEY P'A'TE'NTEDJuL 11 ran 3.676.692

INVENTORS YUKIYASU NISHIKAWA BY TsuNaO HIDAKA 7 A ORNEYS PATENTEDJuu 11912 SHEET OF 4 m5 Q A /4A Z I INVENTORS YUKIYASU NISHIKAWA BY TSUNEOHIDAKA 5 R EYS POSITIONING APPARATUS FOR ARTICLE WITH PORTIONDETERMINING PORTION OF PREDETERMINED CONFIGURATION BACKGROUND OF THEINVENTION The present invention relates to an apparatus for preciselysituating an article at a desired location. For example, the apparatusmay be used for automatically aligning two objects one with respect tothe other.

The invention relates in particular to an apparatus which can detect thedeviation of the article from the desired location in a highly precisemanner so as to achieve a precise positioning of the article when nodeviation from the desired position is detected.

Techniques for accurately aligning a pair of wafer-like objects in apredetermined relationship with respect to each other as well astechniques for aligning a single object with respect to a givenreference, with these positions being deter mined with a high degree ofaccuracy, have been required as in the case where it is desired toachieve precise alignment between a mask and a wafer in the manufactureof integrating circuits or in the achievement of precise alignment forpreventing color deviation during color printing.

Considering, for example, the technique used in the alignment of a maskduring manufacture of integrating circuits, it is known to provideposition-determining marks both for the mask and for the wafer. Thesecomponents are then manually moved until the positioning marks coincide,and during these operations the deviation of the positioning marks fromtheir precision of coincidence is checked through a microscope. Theseoperations require an extremely high degree of skill on the part of theoperator and in addition repetition of the operations for as much as sixor seven times are required during the fabrication of an integrationcircuit, so that many skillful operators are required for thesepurposes, as is wellknown. Attempts have indeed been made to automatethese operations as well as others of the same type used in manydifferent applications, but because of the difficulties encountered indetecting the deviation of the article from the desired position all ofthe proposed solutions to the problem have proved to be of no practicalvalue.

SUMMARY OF THE INVENTION It is accordingly a primary object of theinvention to provide an apparatus which will avoid the above drawbacks.

In particular, it is an object of the present invention to provide foran apparatus used in the positioning of an article a structure whichwill reliably detect in a highly precise manner the deviation of theposition of the article from the required location thereof, so that thisdeviation can be used to determine the proper position of the article.

In particular, it is an object of the present invention to provide anapparatus which uses optical and electrical means to determine thedeviation of an article from its required location with a high degree ofprecision.

Furthermore, it is an object of the invention to provide a constructionof this type which can function not only to determine the deviation inlinear directions but also to determine angular deviation, so that anarticle can be positioned both linearly and angularly.

It is, in particular, an object of the invention to provide aconstruction which while simple and relatively inexpensive neverthelessoperates in a highly reliable manner lending itself to incorporationinto apparatus for automatically determining the precise positioning ofan article either with respect to a given reference or with respect toanother article.

According to the invention, the article whose position is to bedetermined has a positiomdetermining portion of a given configuration. Aprism of the configuration of a truncated pyramid is provided with theopposed end faces of the prism, one of which is smaller than the other,also having the configuration of the position-determining portion of thearticle. A projecting means projects onto the smaller end face of theprism an image of the position-determining portion of the article, andthe of this image from a position of precise alignment with the smallerend face of the prism is detected by a deviation-determining means whichco-acts with the prism. Through this latter means it becomes possible todetect the extent and direction of deviation of the image from therequired position so that the article can have its location changeduntil it is situated precisely at a location where the image of thepositiondetermining portion is in precise alignment with the smaller endface of the prism, thus achieving in a highly accurate manner thedesired location of the article. The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. I is a schematic side elevation of an apparatus of the inventionshown in a plane normal to the Y axis, with the X and Z axes beingillustrated in FIG. 1-,

FIG. 2 is a plan view taken along line A-A of FIG. I in the direction ofthe arrows and schematically illustrating the prism anddeviation-determining means of the invention, with FIG. 2 also show theX and Y axes, and in this case FIG. 2 is normal to the Z axis;

FIGS. 3A 3F, respectively illustrate schematically various position of apositioning image with respect to a prism of the invention;

FIGS. 4A and 4B are respectively graphs showing the current output ofthe apparatus in connection with determination of deviation of an imagefrom the required position;

FIG. 5A is a side elevation of another embodiment of the invention whichis schematically illustrated in FIG. 5 which again shows the mutuallyperpendicular X, Y and Z axes, the plane of FIG. 5A being normal to theX axis;

FIG. 5B is a schematic plan view perpendicular to the Y axis of FIG. 5Aand showing further details of the embodiment of FIG. 5A, FIG. 58 alsoillustrating the X and Z axes; and

FIGS. 6A 6D respectively illustrate various positions of images ofposition-determining portions with respect to the prisms of FIGS. 5A and58.

DESCRIPTION OF PREFERRED EMBODIMENTS The basic arrangement of theapparatus of the invention is illustrated in FIGS. I and 2. By way ofexample, there is illustrated in FIG. I an object I the position ofwhich is to be accurately determined. For this purpose, the object I hasa position-determining portion schematically represented in FIG. I ashaving the configuration of an arrow 5 having a head at its left end, asviewed in FIG. I. The optical properties of the position-determiningportion 5 are such that they will differ sharply from the parts of theobject I surrounding the portion 5. For example, this portion 5 may behighly transparent while the portion of object I surrounding portion 5may be opaque, or the portion 5 may be highly reflecting while the partof object I surrounding the portion Sis substantially less reflecting.Assuming, for example, that the portion 5 is in the form of an openingin the object I of a given configuration, then light from a light source2 will simply travel through this opening.

A projecting means is provided for projecting an image of the portion 5which is uniformly illuminated by the light source 2. This projectingmeans takes the form of a projector lens system 3 schematicallyrepresented and providing a projected image 6 of theposition-determining portion 5.

Referring now to FIG. 2 as well as FIG. I, the apparatus of theinvention further includes a prism 4 having the shape of a truncatedpyramid. In the illustrated example, the prism 4 has opposed end faces42+ and 41- with the end face 42+ being smaller than the end face 42-.These end faces are square and are angularly aligned as well as parallelto each other with these faces being normal to a common optical axiswhich passes perpendicularly and centrally through these end faces ofthe prism 4. The portion 5 in actual practice will have a configurationwhich is the same as that of the end faces of the prism so that theimage 6 will have a configuration matching that of the end face 42+. Ofcourse, the prism 4 has its location fixed by any suitable supportingstructure so that the projected image 6 is precisely focused on thesmaller end face 42+.

Although it is possible to use with the invention prisms of any desiredconfiguration whose end faces match the configuration of theposition-determining portion of the article or object I, such as, forexample, a prism of a truncated triangular configuration or a truncatedpentagonal pyramid for effectively determining the extent of deviationof the image from the required position, the square configurationillustrated is preferred because it provides the simplest possiblecontrols and interrelationship between the detecting system and thecontrols which determine the position of the object or article I.

The illustrated truncated pyramid has, in addition to the flat, parallelend faces 42+ and 42-, four slanting side surfaces 4X+, 4X-, 4Y+, and4Y. The arrangement of these flat sloping side surfaces is clearlyapparent from FIG. 2. Thus, light projected by the optical projector 3toward the smaller end face 42+ will be reflected from the slanting sidesurfaces of the prism. Furthermore, while light will be reflected by thesloping side surfaces, the properties of the prism are such that thelight will pass directly through the flat end faces 42+ and 4Z.

The deviation-detecting means illustrated takes the form of fourphotoelectric elements 7X+, 7X-, 7Y+, and 7Y-, respectively situated inthe path of light reflected from the sloping side surfaces of the prism,in the manner clearly apparent from FIGS. I and 2. Thus, the light whichis focused at a location beyond the end face 4Z+ of the prism 4 will bereflected by the sloping side surfaces to be received by thephotoelectric elements in alignment therewith. On the other hand, thatlight which is directly focused in the form of an image received by thesmaller end face 42+ of the prism 4 is transmitted directly through theprism to exit at the larger end face 42- thereof. The configuration ofthe position-determining portion of the object or article I is such thatit corresponds precisely to the configuration of the end face 42+ of theprism, so that actually in the illustrated example the portion 5 shownschematically as an arrow in FIG. I has the configuration of a squareand may be, for example, an opening of square configuration passingthrough the object or article I and uniformly illuminated from the lightsource 2. In actual practice it has been found best to provide by way ofthe position of the components with respect to each other and theproperties of the projecting means 3 an image 6 the size of which isslightly larger than the size of the smaller end face 4Z+ of the prism4.

The extent of deviation of the image 6 from a position of precisealignment with the end face 42+ is detected by the several photoelectricelements to be transmitted in the form of electrical signals to suitablecontrols 30, schematically represented in FIG. 1, so that these controlscan act through a transmission 32, also schematically represented, forthe purpose of shifting the object or article I automatically until thedeviation of the image 6 from the desired location is detected by thephotoelectric elements as being equal to zero.

The actual operations are illustrated in connection with FIGS. 3 and 4.Thus, assuming that the output currents of the photoelectric elementsare respectively IX+, IX-, IY+ and I( and that the variation of thephotoelectric elements are corrected by a suitable method such as anapplied voltage in the case of photoelectron multiplier tubes, then itis possible to achieve an automatic positioning of the object 1. Inorder to simplify the description it is assumed that thelight-transmission factor within the area of the position-determiningportion 5 through which light passes is 10 times the extent of lighttransmission beyond the outer periphery of the position-determiningportion S, which is to say, beyond the edge which defines theconfiguration of the opening 5. Also, for the sake of simplicity, it isassumed that the deviation direction is only along the X axis. Thus, inFIG. 3A the shaded square 6 represents the location of the image of theposition-determining portion 5 when precise alignment with the smallerend face 4Z+ of the prism 4 is achieved. Thus, assuming that the lightintensity of the light providing the image 6 is 10 times that of thearea surrounding the position-determining portion 5, then a clear image6 will be projected onto the prism in the manner shown schematically inFIGS. 3A 3E. In the final precisely determined non -deviation positionof the image shown in FIG. 3A, the intensities of the light received bythe photoelectric elements TX-iand 7X- are equal to each other while inthe case of a deviation in the direction +X, the intensity of lightreceived by the photoelectric element 7X+ is greater than that receivedby the opposite photoelectric element 7X. Thus, as the image 6 is shownprogressively deviating to a greater extent from the position of FIG. 3Ain the several positions FIG. 38 FIG. 3B, the greater light intensity ofthe image 6 will provide for the photoelectric element 7X+ at differentelectrical output than that for the photoelectric element 7X. The outputcurrents which can be achieved through such elements are illustrated inthe graphs of FIGS. 4A and 48. FIGS. 4A and 4B illustrate the outputcurrents IX+ and IX- of the photoelectric elements 7X+ and 7X,respectively, together with the output current differential (IX+ IX-),based on the intensity of the light received by the photoelectricelements 7X+ and 7X under the conditions respectively illustrated inFIGS. 3A 3E. Thus, referring to FIG. 4A, the output currentscorresponding to FIG. 3A are illustrated at the region A of the graph.It will be noted that when progressing to the right through the regionsof the graph corresponding to FIGS. 3B and 3C, the output current ofphotoelectric element 71(- diminishes slightly and remains at a constantlow value while the output current of photoelectric element 7X+increases to reach a maximum at the area of the graph C corresponding toFIG. 3C. At this time, the most intensely illuminated image 6 extendscompletely across the sloping surface 4X+ which reflects light to theelement 7X+. Then when the image shifts further through the position ofFIG. 3D and into the position of FIG. 3E, the output currents change asillustrated at the right portion of FIG. 4A. In this way, detection ofdeviation can be very accurately determined.

FIG. 4B shows the reverse arrangement of FIG. 4A in that with FIG. 4Bthe position-determining portion 5, instead of providing a lightintensity 10 times as great as that of the surrounding area of theobject or article provides a light intensity which is one-tenth of thesurrounding area of the object or article. In other words, it is onlyimportant that there be a sharp contrast in the light-transmitting orlight-reflecting properties of the position-determining portion 5 andthe surrounding area of the object. Thus, with FIG. 4B the outputcurrents are those which will result when the position-determiningportion 5 has a transmission factor which is one-tenth of thesurrounding light-transmission factor.

As is apparent from FIGS. 4A and 43, it is possible to detect deviationboth with respect to extent and direction from the difference betweenthe output currents of the opposed photoelectric elements within therange where the projected image of the position-determining portion atleast partly overlaps the prism which has the truncated pyramid shapeillustrated. In addition, a detection sensitivity l/AX A(IX+ lX)relative to a slight amount of deviation AX is sharply greater at theregion where the precise coincidence or desired location of the imagesand of the article is achieved. It is therefore clear that a higherdegree of accuracy in the positioning of the object is achieved whenusing these detection operations for the automatic alignment apparatus30 which is schematically represented in FIG. I.

In the case of angular deviation, schematically represented in FIG. 3F,the sensitivity of the detection is somewhat reduced but nevertheless itis still possible with the abovedescribed apparatus to detect adeviation from the required position so that accurate location of theimage and the object can be achieved in this case also.

While the above description has dealt with deviation in the X direction,deviation in the Y direction is simultaneously detected based upon theoutput current differential (IY+- lY) with respect to the other pair ofphotoelectric elements 7Y+ and 7Y, as was the case with deviation in theX direction. Also, it is possible to provide an optical system forachieving a reflected image when the position-determining portion 5 isdesigned as a reflecting surface having a reflecting factorsubstantially different from that of the surrounding area of the object.In this case also it is possible to detect the deviation in the same wayas when the light is transmitted through a transparent portion.

A further embodiment of the invention is illustrated in FIGS. 5A and SB,and this embodiment is particularly useful for achieving angularpositioning of an article as well as longitudinal and transversalpositioning thereof. FIGS. 5A and 5B are specifically directed to theapparatus as embodied in mask alignment during fabrication ofintegration circuits. Referring to FIGS. 5A and 5B, the mask 8 is to beused for subsequent exposure. A semi-transparent mirror 10 transmitsilluminating light and at the same time partially reflects lightreflected by a wafer 9 to the deviation-detecting system. Anillumination source I2 is provided for a source of light used forpositioning purposes while a second source of light 13 is used forexposure purposes. The mirror ll is rotatable between the positionillustrated in FIG. 5A where it interrupts light from the exposure lampl3 and reflects light from the lamp l2 to a position where it permitslight from the lamp 1?: to pass so as to be used for exposure purposes.In this way, a changeover between the light sources 12 and I3 isachieved.

The mask 8 is formed with a pair of position-determining portions 18Aand 18B in the form of square openings passing through the mask 8 andlocated thereon as illustrated in FIG. 5B. A pair of detecting systemsare provided for respectively coacting with the pair ofposition-determining means 18A and 18B. These detecting systems includethe pair of optical projecting means having the enlarging projectinglens systems 14A and MB. In addition, the optical systems include thepair of prisms 16A and 168 each of which is of the truncatedconfiguration described above in connection with the prism 4 so thatthese prisms 16A and 16B have smaller square end faces toward whichimages of position-determining portions 18A and 18B are projected by thepair of optical projecting means MA and 148. Four photoelectric elements17AX+, i7AX-, I7Ay+ and I'TAY- are respectively positioned opposite andin alignment with the slanting side surfaces of the prism USA to receivelight reflected by the latter surfaces, and four photoelectric elementsI7BX+, l7BX-, I7BY+ and "BY- are respectively positioned opposite thesloping side surfaces of the prism 16B to receive light reflected fromthe latter surfaces. The prisms ISA and B are provided simply to spreadthe optical axes apart from each other so that the paths of light travelfrom the pair of position-determining means 18A and 188 will be locatedat a greater distance from each other. In this way it becomes possibleto arrange in a very convenient manner the pair of prisms 16A and 16Band the several photoelectric elements coacting therewith. It will benoted that with this arrangement, the distance between the prisms 16Aand l6B can be considerably greater than that between theposition-determining portions 18A and 188.

The mask 8 is positioned after adjustment in such a way that enlargedimages of the portions ISA and 18B respectively coincide with thesmaller end faces of the prisms MA and 168. It is assumed that the areaswithin the portions 18A and 18B are transparent in that these portionsare in the form of simple openings of square configuration passingthrough the mask while the parts of the latter surrounding the openings18A and 18B are black and opaque. FIG. 6A shows the pair of prisms 16Aand 168 with the shaded areas surrounding the bright images which aredirected onto the prisms. Thus, the shaded areas of prisms 16A and 16Brepresent the opaque or black portions surrounding the portions 18A and188 through which light travels to achieve the square images which arein IAY+ lAY- 0 IBY+ IBY- 0 lAX+ IAX- 0 IBX+ IBX- 0 lAX+ IBX+ 0 In theabove listing, the several output currents are those of the eightphotoelectric elements respectively situated opposite the slopingsurfaces of the prisms.

It is possible with this arrangement to achieve a higher accuracy byproviding on the wafer 9 additional position-determining portions HA and198 in the form of light-reflecting marks which are of a squareconfiguration matching the configurations of the position-determiningportions l8A and 183 but which will provide smaller images which can beprecisely aligned centrally within the images of the portions 18A andIBB. The distance between the portions 19A and I98 is of course equal tothat between the portions 18A and 188 on the mask. However, theseportions 19A and 19B are smaller than the portions 18A and 188 whilehaving a matching configuration. Therefore, all of these portions are ofa square configuration in the illustrated example. The arrangement issuch that the reflected images of the portions 19A and l9B will be justslightly larger than the areas of the smaller end faces of the prisms.It is assumed that for the convenience of explanation the reflectionfactors of the portions HM and 19B are smaller than those at the outerperipheries or beyond the outer peripheries thereof, respectively.

Thus, the wafer 9 is positioned beneath the mask 8 in such a manner thatthe portions 19A and 19B are at least partially visible through theportions [8A and 18B on the mask 8. This may be achieved, for example,by placing a linear edge of the wafer (i.e., orientation flat) against asuitable reference surface. FIG. 68 illustrates by way of example theimages projected with the components in this position. In FIG. 6B theinner shaded areas within the images of the openings 18A and 18Brepresent at least parts of the reflected images of the portions [9A and193. The output currents of the several photoelectric elements arecompared with each other and the structure operates automatically toprovide for the wafer 9 a rotary position which is controlled in such away as to establish:

With this latter set of relationships, the position shown in FIG. 6C isachieved. At this time, there is equality in the illumination at theprism by the images projected thereon, but the inner images formed byportions 19A and 19B are still not precisely positioned. To achieve thislatter precise positioning the controls continue to operate in thedirections X and Y to bring about the perfected alignment between theportions 18A and 188 on mask 8 and portions 19A and 198 on wafer 9, asillustrated with the image positions in FIG. 6D. This procedure for maskalignment is applicable not only with respect to mask alignment incontact exposure techniques as referred to above, but also in theenlarged projection exposure technique.

It is apparent from the above description that the invention may be usedfor detection of deviation in automatic alignment apparatus with thefollowing advantages:

l. The use of the prism of truncated square pyramidal configurationfacilities detection of deviation in two dimensions, or in other words,along a pair of mutually perpendicular axes. The signals which areobtained are easily coupled with the control system due to the distinctdirection of the deviation. Higher accuracy of alignment can be attainedwhere the photoelectric element and the amplifier both have a relativelynarrow range of operation inasmuch as a detection sensitivity is sharplyhigher adjacent the point when precise alignment is achieved while it issubstantially lower within an area of a substantial deviation from therequired position.

2. An arrangement where the image focused at the smaller end face of thetruncated prism may be observed when viewing the latter through thelarger face thereof provides the possibility of various additionalfunctions referred to below without any interception of the light pathin the optical system for detecting the deviation. It is possible, forexample, to detect the state of the alignment with the naked eye byobserving the projected image if cross hairs are provided not onlyintersecting at the center of the larger end face of the truncatedpyramid which forms the prism but also at the center of theposition-determining portion. The possibility of this latter operationis of great advantage for balancing the adjustment of each photoelectricelement. Furthermore, deviation along three mutually perpendicular axesis also possible by detecting the manner in which the image is focusedat the smaller end face of the prism. Thus, it can be detected whetherthe image is focused precisely at the smaller end face of the prism orat a location relatively near to or relatively far from the smaller endface of the prism, so that in this way deviations not only along the Xand Y axes but along the Z axis can be detected.

What is claimed is:

i. In an apparatus for positioning an article which has at least oneposition-determining portion of a predetermined polygonal configuration,at least one prism having the shape of a truncated pyramid and includinga pair of opposed end faces one of which is smaller than the other andboth of which have said predetermined configuration, said end faces ofsaid truncated pyramid being angularly aligned, and said truncated prismhaving slanting side surfaces extending between said end faces from theedge of the smaller to the edge of the larger of said end faces, saidend faces being parallel and perpendicular to a common optical axispassing centrally through said end faces, projecting means coacting withsaid prism for projecting onto said smaller end face an image of saidposition-determining portion of the article, the latter article beingprecisely situated in a desired location when the image of saidposition-determining portion is precisely aligned axially and angularlywith respect to the axis of the prim and with said smaller of the endfaces of said prism, and deviation-determining means for determining theextent to which the location of said image deviates from a position ofprecise alignment with said smaller end face of said prism.

2. The combination of claim 1 and wherein said polygonal configurationis a regular polygon.

3. The combination of claim 2 and wherein said projecting means providesfor said position-determining portion of the article an image whosemagnitude is at least as great as that of said smaller end face of saidprism.

4. The combination of claim 3 and wherein said projecting means providesfor said image a magnitude which is slightly greater than that of saidsmaller end face of said prism, so that when said image is preciselypositioned with respect to said smaller end face, the peripheral regionsof said image extend onto the regions of said slanting prism surfaceswhich adjoin said smaller end face.

5. The combination of claim 3 and wherein said deviationdeterminingmeans includes a plurality of photoelectric elements positioned in thepath of light reflected from said slanting side surfaces of said prism,respectively, for providing signals which can be compared in accordancewith the differences in light received by said photoelectric elementsfor determining the extent and direction of deviation of said image fromthe position of precise alignment with said smaller end face of saidprism, so that the article can have its position changed until all ofthe photoelectric elements receive uniform amounts of light indicatingprecise alignment of said image with said smaller end face of saidprism.

6. The combination of claim I and wherein the article has a air ofspacedposition-determining portions of said confi uraion, there being apan of said prisms and a pair of ear projecting means respectivelyprojecting images of said positiondetermining portions onto the smallerend faces of said prisms, whereby precise alignment of said images withsaid smaller end faces of said prisms will angularly orient the article.

'7. The combination of claim I and wherein the positiondeterminingportion of the article is in the form of an opening of saidpredetermined configuration, so that light passing through said openingis projected by said projecting means onto said smaller end face of saidprism to provide said image the configuration of which corresponds tothat of said opening, and an additional position-determining elementsituated in alignment with said opening for reflecting lighttherethrough and having a configuration which will provide a reflectedimage of said additional position-determining element smaller than thatof said opening so that when the reflected image is aligned within thelarger image of said opening, a precise determination of the location ofthe article is achieved.

8. The combination of claim I and wherein said configuration is that ofa square, said prism having square end faces and four slanting flatsides extending therebetween, and said deviation-determining meansdetermining the deviation of said image with respect to at least a pairof mutually perpendicular axes.

9. The combination of claim 8 and wherein said deviationdeterminingmeans includes photoelectric elements respectively situated oppositesaid four slanting sides for receiving light reflected therefrom todetermine the deviation of the image along said pair of mutuallyperpendicular axes.

t 1 i i i

1. In an apparatus for positioning an article which has at least oneposition-determining portion of a predetermined polygonal configuration,at least one prism having the shape of a truncated pyramid and includinga pair of opposed end faces one of which is smaller than the other andboth of which have said predetermined configuration, said end faces ofsaid truncated pyramid being angularly aligned, and said truncated prismhaving slanting side surfaces extending between said end faces from theedge of the smaller to the edge of the larger of said end faces, saidend faces being parallel and perpendicular to a common optical axispassing centrally through said end faces, projecting means coacting withsaid prism for projecting onto said smaller end face an image of saidposition-determining portion of the article, the latter article beingprecisely situated in a desired location when the image of saidposition-determining portion is precisely aligned axially and angularlywith respect to the axis of the prim and with said smaller of the endfaces of said prism, and deviation-determining means for determining theextent to which the location of said image deviates from a position ofprecise alignment with said smaller end face of said prism.
 2. Thecombination of claim 1 and wherein said polygonal configuration is aregular polygon.
 3. The combination of claim 2 and wherein saidprojecting means provides for said position-determining portion of thearticle an image whose magnitude is at least as great as that of saidsmaller end face of said prism.
 4. The combination of claim 3 andwherein said projecting means provides for said image a magnitude whichis slightly greater than that of said smaller end face of said prism, sothat when said image is precisely positioned with respect to saidsmaller end face, the peripheral regions of said image extend onto theregions of said slanting prism surfaces which adjoin said smaller endface.
 5. The combination of claim 3 and wherein saiddeviation-determining means includes a plurality of photoelectricelements positioned in the path of light reflected from said slantingside surfaces of said prism, respectively, for providing signals whichcan be compared in accordance with the differences in light received bysaid photoelectric elements for determining the extent and direction ofdeviation of said image from the position of precise alignment with saidsmaller end face of said prism, so that the article can have itsposition changed until all of the photoelectric elements receive uniformamounts of light indicating precise alignment of said image with saidsmaller end face of said prism.
 6. The combination of claim 1 andwherein the article has a pair of spaced position-determining portionsof said configuration, there being a pair of said prisms and a pair ofsaid projecting means respectively projecting images of saidposition-determining portions onto the smaller end faces of said prisms,whereby precise alignment of said images with said smaller end faces ofsaid prisms will angularly orient the article.
 7. The combination ofclaim 1 and wherein the position-determining poRtion of the article isin the form of an opening of said predetermined configuration, so thatlight passing through said opening is projected by said projecting meansonto said smaller end face of said prism to provide said image theconfiguration of which corresponds to that of said opening, and anadditional position-determining element situated in alignment with saidopening for reflecting light therethrough and having a configurationwhich will provide a reflected image of said additionalposition-determining element smaller than that of said opening so thatwhen the reflected image is aligned within the larger image of saidopening, a precise determination of the location of the article isachieved.
 8. The combination of claim 1 and wherein said configurationis that of a square, said prism having square end faces and fourslanting flat sides extending therebetween, and saiddeviation-determining means determining the deviation of said image withrespect to at least a pair of mutually perpendicular axes.
 9. Thecombination of claim 8 and wherein said deviation-determining meansincludes photoelectric elements respectively situated opposite said fourslanting sides for receiving light reflected therefrom to determine thedeviation of the image along said pair of mutually perpendicular axes.